Disruptions of social affiliative and emotional behaviors are among the earliest-onset symptoms of schizophrenia, often beginning during adolescence or sometimes late childhood. The neurobiological mechanisms of these lifelong social behavior disabilities of schizophrenia are poorly understood, and effective treatments are lacking. However, multiple lines of evidence suggest that NMDA signaling and epigenetic mechanisms in amygdala circuits play important roles in early social behavior development. Project II will test the overall hypothesis that disruption of NMDA receptor signaling in basolateral amygdala (BLA) will disrupt early development of socioemotional behaviors, and that pharmacologic modulation of GABA signaling or epigenetic marks will rescue sociability development. Specific Aim 1: Determine the role of amygdala NMDA signaling in early development of socioemotional behaviors. Using behavioral studies of NMDA NR1 hypomorph mice or mice with amygdala-specific deletions of NMDA NR1, we will test the hypotheses that disruption of NMDA receptors in the amgydala will lead to reduced sociability in the social choice test, impaired fear conditioning, and reduced reward seeking behaviors starting in prepubescence, and that a GABA-B agonist or an HDAC inhibitor will rescue sociability development. Specific Aim 2: Determine the role of BLA cell types and epigenetic mechanisms in early development of social affiliative behaviors. Using double-labeling immunohistochemistry (Fos with markers of GABAergic or glutamatergic neurons) and Chip-Seq, we will test the hypothesis that mice with reduced sociability will show reduced activation of BLA GABAergic interneurons during social interactions, as well as increased DNA methylation and decreased histone acetylation in the BLA. Specific Aim 3: Determine the physiological activation of BLA in NMDA NR1 mutants across early development. We will test the hypothesis that NMDA NR1 hypomorphs will show decreased inhibition of BLA activity by stimulation of glutamatergic afferents to BLA, and that the relevant afferents will be primarily thalamus-BLA prior to puberty and prefrontal-BLA after puberty. These mechanistic studies may lead to development of novel treatments for negative symptoms of schizophrenia.